Major UI refresh: sidebar redesign, theme expansion, and chat performance optimizations (#706)

## Summary
Complete sidebar redesign and comprehensive UI polish pass with performance optimizations, theme system refinements, and desktop integration improvements.

## Key Changes

**Sidebar & Navigation Redesign**
- Redesigned sessions sidebar layout with unified button primitives
- Added activity sections with project grouping and improved session organization
- Refined sidebar corners, spacing, and visual hierarchy
- Removed NavRail component in favor of streamlined sidebar
- Stabilized sessions bar toggle position in fullscreen mode

**Performance Optimizations**
- Reduced chat streaming CPU usage and storage churn
- Optimized task tool polling and live timers with debouncing
- Prevented chat state races and reduced background request load
- Debounced draft writes and coalesced session reloads
- Optimized message store updates and turn tracking

**Theme & Visual System**
- Added theme-aware window corners (desktop) and border radius tokens
- Introduced glassmorphism effects on desktop sidebar
- Added backdrop blur to UI elements

**Chat Experience**
- Added session-based permission auto-accept toggle in chat input
- Polished permission shield UX with improved icon sizing and spacing
- Fixed chat scroll-to-bottom behavior and timeline tracking
- Enhanced tool output display with better path label detection
- Removed duplicate draft context details in chat header
- Added text selection menu to chat messages

**Git Improvements**
- Refreshed git history visual design with cleaner dividers
- Added remote removal action in sync selector
- Stabilized git polling to prevent excessive requests
- Improved tool output rendering for git operations

**Settings & Panels**
- Fixed mobile scrolling on settings pages
- Made outside-click settings close instantly
- Reduced settings load churn and CPU spikes
- Improved services dropdown layout and spacing
- Softened panel resize handles

**Desktop Integration**
- Synced macOS window theme with app theme
- Restored window dragging in sidebar header zones
- Fixed system window corners on macOS
- Improved header session metadata and action controls

**Button & Component Standardization**
- Unified button primitives across all components
- Standardized destructive action patterns
- Removed unused button variants (button-large, button-small)
- Aligned context tab close hit areas

---------

Co-authored-by: Iuliia Ivashko <yulia.ivashko@gmail.com>

packages/ui/src/components/session/sidebar/SidebarFooter.tsx

@@ -0,0 +1,42 @@
+import React from 'react';
+import { RiInformationLine, RiQuestionLine, RiSettings3Line } from '@remixicon/react';
+import { Tooltip, TooltipContent, TooltipTrigger } from '@/components/ui/tooltip';
+
+type Props = {
+  onOpenSettings: () => void;
+  onOpenShortcuts: () => void;
+  onOpenAbout: () => void;
+};
+
+const footerButtonClassName = 'inline-flex h-8 w-8 items-center justify-center rounded-md text-muted-foreground hover:bg-interactive-hover/50 hover:text-foreground focus-visible:outline-none focus-visible:ring-2 focus-visible:ring-primary/50';
+
+export function SidebarFooter({ onOpenSettings, onOpenShortcuts, onOpenAbout }: Props): React.ReactNode {
+  return (
+    <div className="flex shrink-0 items-center justify-start gap-1 px-2.5 py-2">
+      <Tooltip>
+        <TooltipTrigger asChild>
+          <button type="button" onClick={onOpenSettings} className={footerButtonClassName} aria-label="Settings">
+            <RiSettings3Line className="h-4.5 w-4.5" />
+          </button>
+        </TooltipTrigger>
+        <TooltipContent side="top" sideOffset={4}><p>Settings</p></TooltipContent>
+      </Tooltip>
+      <Tooltip>
+        <TooltipTrigger asChild>
+          <button type="button" onClick={onOpenShortcuts} className={footerButtonClassName} aria-label="Shortcuts">
+            <RiQuestionLine className="h-4.5 w-4.5" />
+          </button>
+        </TooltipTrigger>
+        <TooltipContent side="top" sideOffset={4}><p>Shortcuts</p></TooltipContent>
+      </Tooltip>
+      <Tooltip>
+        <TooltipTrigger asChild>
+          <button type="button" onClick={onOpenAbout} className={footerButtonClassName} aria-label="About OpenChamber">
+            <RiInformationLine className="h-4.5 w-4.5" />
+          </button>
+        </TooltipTrigger>
+        <TooltipContent side="top" sideOffset={4}><p>About OpenChamber</p></TooltipContent>
+      </Tooltip>
+    </div>
+  );
+}